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Diffstat (limited to 'man/man2/ioctl_iflags.2')
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diff --git a/man/man2/ioctl_iflags.2 b/man/man2/ioctl_iflags.2 new file mode 100644 index 000000000..0f4c533bc --- /dev/null +++ b/man/man2/ioctl_iflags.2 @@ -0,0 +1,202 @@ +.\" Copyright (c) 2017 by Michael Kerrisk <mtk.manpages@gmail.com> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.\" +.TH ioctl_iflags 2 (date) "Linux man-pages (unreleased)" +.SH NAME +ioctl_iflags \- ioctl() operations for inode flags +.SH DESCRIPTION +Various Linux filesystems support the notion of +.IR "inode flags" \[em]attributes +that modify the semantics of files and directories. +These flags can be retrieved and modified using two +.BR ioctl (2) +operations: +.P +.in +4n +.EX +int attr; +fd = open("pathname", ...); +\& +ioctl(fd, FS_IOC_GETFLAGS, &attr); /* Place current flags + in \[aq]attr\[aq] */ +attr |= FS_NOATIME_FL; /* Tweak returned bit mask */ +ioctl(fd, FS_IOC_SETFLAGS, &attr); /* Update flags for inode + referred to by \[aq]fd\[aq] */ +.EE +.in +.P +The +.BR lsattr (1) +and +.BR chattr (1) +shell commands provide interfaces to these two operations, +allowing a user to view and modify the inode flags associated with a file. +.P +The following flags are supported +(shown along with the corresponding letter used to indicate the flag by +.BR lsattr (1) +and +.BR chattr (1)): +.TP +.BR FS_APPEND_FL " \[aq]a\[aq]" +The file can be opened only with the +.B O_APPEND +flag. +(This restriction applies even to the superuser.) +Only a privileged process +.RB ( CAP_LINUX_IMMUTABLE ) +can set or clear this attribute. +.TP +.BR FS_COMPR_FL " \[aq]c\[aq]" +Store the file in a compressed format on disk. +This flag is +.I not +supported by most of the mainstream filesystem implementations; +one exception is +.BR btrfs (5). +.TP +.BR FS_DIRSYNC_FL " \[aq]D\[aq] (since Linux 2.6.0)" +Write directory changes synchronously to disk. +This flag provides semantics equivalent to the +.BR mount (2) +.B MS_DIRSYNC +option, but on a per-directory basis. +This flag can be applied only to directories. +.\" .TP +.\" .BR FS_EXTENT_FL " \[aq]e\[aq]" +.\" FIXME Some support on ext4? (EXT4_EXTENTS_FL) +.TP +.BR FS_IMMUTABLE_FL " \[aq]i\[aq]" +The file is immutable: +no changes are permitted to the file contents or metadata +(permissions, timestamps, ownership, link count, and so on). +(This restriction applies even to the superuser.) +Only a privileged process +.RB ( CAP_LINUX_IMMUTABLE ) +can set or clear this attribute. +.TP +.BR FS_JOURNAL_DATA_FL " \[aq]j\[aq]" +Enable journaling of file data on +.BR ext3 (5) +and +.BR ext4 (5) +filesystems. +On a filesystem that is journaling in +.I ordered +or +.I writeback +mode, a privileged +.RB ( CAP_SYS_RESOURCE ) +process can set this flag to enable journaling of data updates on +a per-file basis. +.TP +.BR FS_NOATIME_FL " \[aq]A\[aq]" +Don't update the file last access time when the file is accessed. +This can provide I/O performance benefits for applications that do not care +about the accuracy of this timestamp. +This flag provides functionality similar to the +.BR mount (2) +.B MS_NOATIME +flag, but on a per-file basis. +.\" .TP +.\" .BR FS_NOCOMP_FL " \[aq]\[aq]" +.\" FIXME Support for FS_NOCOMP_FL on Btrfs? +.TP +.BR FS_NOCOW_FL " \[aq]C\[aq] (since Linux 2.6.39)" +The file will not be subject to copy-on-write updates. +This flag has an effect only on filesystems that support copy-on-write +semantics, such as Btrfs. +See +.BR chattr (1) +and +.BR btrfs (5). +.TP +.BR FS_NODUMP_FL " \[aq]d\[aq]" +Don't include this file in backups made using +.BR dump (8). +.TP +.BR FS_NOTAIL_FL " \[aq]t\[aq]" +This flag is supported only on Reiserfs. +It disables the Reiserfs tail-packing feature, +which tries to pack small files (and the final fragment of larger files) +into the same disk block as the file metadata. +.TP +.BR FS_PROJINHERIT_FL " \[aq]P\[aq] (since Linux 4.5)" +.\" commit 040cb3786d9b25293b8b0b05b90da0f871e1eb9b +.\" Flag name was added in Linux 4.4 +.\" FIXME Not currently supported because not in FS_FL_USER_MODIFIABLE? +Inherit the quota project ID. +Files and subdirectories will inherit the project ID of the directory. +This flag can be applied only to directories. +.TP +.BR FS_SECRM_FL " \[aq]s\[aq]" +Mark the file for secure deletion. +This feature is not implemented by any filesystem, +since the task of securely erasing a file from a recording medium +is surprisingly difficult. +.TP +.BR FS_SYNC_FL " \[aq]S\[aq]" +Make file updates synchronous. +For files, this makes all writes synchronous +(as though all opens of the file were with the +.B O_SYNC +flag). +For directories, this has the same effect as the +.B FS_DIRSYNC_FL +flag. +.TP +.BR FS_TOPDIR_FL " \[aq]T\[aq]" +Mark a directory for special treatment under the Orlov block-allocation +strategy. +See +.BR chattr (1) +for details. +This flag can be applied only to directories and +has an effect only for ext2, ext3, and ext4. +.TP +.BR FS_UNRM_FL " \[aq]u\[aq]" +Allow the file to be undeleted if it is deleted. +This feature is not implemented by any filesystem, +since it is possible to implement file-recovery mechanisms outside the kernel. +.P +In most cases, +when any of the above flags is set on a directory, +the flag is inherited by files and subdirectories +created inside that directory. +Exceptions include +.BR FS_TOPDIR_FL , +which is not inheritable, and +.BR FS_DIRSYNC_FL , +which is inherited only by subdirectories. +.SH STANDARDS +Linux. +.SH NOTES +In order to change the inode flags of a file using the +.B FS_IOC_SETFLAGS +operation, +the effective user ID of the caller must match the owner of the file, +or the caller must have the +.B CAP_FOWNER +capability. +.P +The type of the argument given to the +.B FS_IOC_GETFLAGS +and +.B FS_IOC_SETFLAGS +operations is +.IR int\~* , +notwithstanding the implication in the kernel source file +.I include/uapi/linux/fs.h +that the argument is +.IR long\~* . +.SH SEE ALSO +.BR chattr (1), +.BR lsattr (1), +.BR mount (2), +.BR btrfs (5), +.BR ext4 (5), +.BR xfs (5), +.BR xattr (7), +.BR mount (8) |